Our small metal boat glides through the current as it snakes between steep sandstone cliffs. Tucked between America’s two largest reservoirs, the stretch of the Colorado River that lies north-east of the Grand Canyon is cool and calm. As the water glimmers in the early morning light, it is easy to forget this serene waterway has been named the most endangered in the US.
But as we round a bend, a shadow envelops the boat and Glen Canyon Dam comes into view – 4.9m cubic yards of concrete ominously arching 710ft into a cloudless sky. “This is as close as we can get,” says Ted Kennedy, a biologist and one of my guides for the day, as he cuts the engine.
The dam marks the starting point of a day-long scientific journey down the river with a team of federal scientists from the US Geological Survey (USGS) – hydrologists, biologists, ecologists and archaeologists – who are intimately familiar with how human hands have shaped this once wild basin. They have been tasked with finding ways to help natural systems thrive in this altered landscape.
The Colorado River has long been caught in a delicate balancing act – part resource, part wilderness. Now, the stakes are rising. As the climate crisis creates new challenges, tensions between states and the increasing needs of those who hold rights to this water are pushing the riparian ecosystems into dangerous new territory.
Already, ecologically important sandbars that line the river’s banks are shrinking, starved of sediment held back by the dam. Native fish populations are threatened along with the insects and invertebrates they feed on, a new mix of plant species is taking root, and ancient artifacts tucked into the canyons are becoming more exposed. Things will only worsen as the water supply wanes.
Divided between the boats, and armed with printed pages of data, floating equipment, and lots of snacks, we launch from Lees Ferry, 15 miles downriver from the dam, where scores of kayakers and rafting guides are ready for a day of play. An important juncture for recreation on the river – just before the first rapids in the Grand Canyon – it’s also where flows are measured to ensure accurate distribution of the Colorado’s prized water to lower-basin states.
But for these scientists, this is part of a living laboratory. Experiments here will help inform the difficult decisions that will define the river’s future, just as it grows more precarious.
‘You pull on one thread … ’
Glen Canyon Dam is the most blatant example of human intrusion, but not the only one.
Above us, tourists cluster on the ridgeline. Kayaks coast past tents dotting the sandy shore. Ancient petroglyphs etched into the cliffside roughly 3,000 years ago are now faintly accompanied by the name “Travis”, carved and then colored in with charcoal.
But altering the way this stretch of river runs had the most profound impact on the species that once thrived here. In the decades since the Glen Canyon Dam and the Hoover Dam further downstream were constructed, the infrastructure has become a controversial but important part of a vast system that waters the west, creating the massive reservoirs of Lake Powell and Lake Mead. The river’s water sustains 40 million people and Glen Canyon Dam provides hydroelectric power across seven states.
It’s also caused irreparable harm to the ecosystems around it by forever altering the Colorado River’s flow.
While annual flow must remain steady to abide by water distribution agreements, in the post-dam era, short-term surges of water are determined by the region’s daily demand for hydroelectric energy. To generate that power, water is released from Lake Powell through Glen Canyon Dam at regulated intervals, creating an unnatural flow for the river on the other side. Water levels can vary wildly from day to day, while sediment that would normally travel along the river is held back, causing riverbanks to shrink and the water to run clear.
The result has been a disruption of what scientists refer to as the food web – a layered chain of consumption and a key indicator of a river’s ability to sustain vibrant and diverse life. Populations of native fish species, including the humpback chub, are in greater danger as conditions increasingly favor new predators, amid declines in the diversity of the insects and invertebrates they feed on.
“All these things are connected,” says Kennedy. “You pull on one thread and it is often hard to predict what is connected to it.”
Kennedy, clad in a bright orange USGS long-sleeve, always manages to offer complex scientific analysis with amiable explanations. But he is especially concerned about the invertebrates that form the foundation of this food web. Their numbers are extremely low in the Grand Canyon area, ranking in the bottom 10% of rivers worldwide.
“Aquatic insects are indicators of a river’s ability to support life,” Kennedy says. Without diversity, a river becomes less resilient to sweeping changes, like those fueled by the climate crisis.
The issue has been amplified by the unnatural water flow from the dam, which creates artificial morning and evening tides. When water levels get too low, it can harm the reproduction cycles of aquatic insects who lay their eggs on rocks underwater at the river’s edge. “These eggs are getting dried out and desiccated every day with these tides,” he says.
The changed flow has also affected plants by creating conditions that favor some species over others. Those that need to photosynthesize have moved into the clean water, after the dam cleared this part of the river’s natural heavy brown tinge. Which plants can thrive now depends on decisions made by water managers, the balance between wilderness and resource in stark relief once again.
As the boat churns around the bend of the river and slows, the ecologist Emily Palmquist jumps off into a marshy eddy. “All the ecosystems we work in are changed ecosystems,” she says. Mud squelches and stems crunch beneath her as she walks across the inlet, crowded with an abundance of greenery.
Naming each plant and distinguishing between native varieties, Palmquist points to the mix of textures and species growing on the shoreline and in the sand that slopes against the rock face above. Those that can withstand having their roots constantly flushed survive along the water’s edge. Others, farther back, possess a system of tap roots that enable them to dig deep beneath the soil to access water.
“Humans are part of this landscape and we have been for a long time. It is just a matter of what people as a society want it to look like, how much we are willing to manage it, and what we are willing to sacrifice to have one thing or the other,” she says.
But it’s not just plants and animals put at risk. Archaeological sites considered sacred by Indigenous nations dot the dramatic landscapes, long shielded from the elements and kept out of sight from curious and destructive tourists. Without an abundance of sand or sediment coming downriver to recoat them, erosion is leaving them increasingly exposed. Indigenous communities and scientists now fear they run a greater risk of being destroyed.
It is nearing lunchtime and the sun sits high in the sky when we spot clusters of rafts tied off along the shore. There, tour guides lead throngs of visitors on a short walk across the embankment to a spot where ancient petroglyphs are on open display. The scientists make their way along the unshaded trail, blending in with campers and sunburned teenagers.
Helen Fairley, a USGS social scientist, points out neatly sketched sheep with large horns, probably left there more than 3,000 years ago. Access to these historic wall drawings, she says, is meant to satisfy onlookers so they don’t go in search of more concealed sites now showing themselves as the cliff sides and sandbanks erode.
Steps toward survival
Working within a changed ecosystem means scientists must accept the limits of what they can control. Much of their effort comes down to measuring and tinkering with water flow.
Just 15 miles downriver from the dam, near the Lees Ferry boat ramp, flows are carefully monitored to ensure the right amount passes through for use by Arizona, Nevada and California.
From the boat, the hydrologist Jessica Anderson uses a device resembling a futuristic boogie board that scans the current and sends measurements back to an onboard computer. “One cubic foot per second is roughly the size of a basketball,” she says. “So this is like 19,000 basketballs going by every second.” Another way to picture it: the river at this juncture would fill an Olympic-sized swimming pool in just five seconds.
Before Glen Canyon Dam, the river ebbed and flowed with the seasons, surging during the spring snowmelt and slowing as water levels waned. The roughly 60m tons of sediment carried through the system was deposited and dispersed, creating important habitats, recreation spots and a dynamism needed to sustain the river’s wild nature.
“The dam completely changed the flow regime,” the research hydrologist Paul Grams says, stepping off his boat into the shallows.
To help restore the balance, scientists are now playing with the timing and intensity of releases. Without altering the annual amount of water flowing through the system, they found they could still re-create smaller surges and “fake floods” that mimic a more natural flow.
It’s already had a profound impact. High flows were found to be effective at redistributing sediment and rebuilding the washed-out riverbanks, especially when timed to coordinate with the input of sediment from tributaries along the river. “If you don’t erode the sandbars and then rebuild them, [the river] becomes static and you get more and more of the river becoming canal-like and stagnant,” says Grams.
A separate set of experiments found a low flow, which released a slower and more consistent current during certain times of the year, could better protect insects’ eggs and give native plant species more opportunity to take root.
“One of the sensitive insects, caddisflies, ended up increasing by 400% during the so-called ‘bug flow’ years compared to the six-year baseline,” Kennedy says of his experiment with water flow. Meanwhile, algae, which Kennedy says is an important feature at the base of the food web, increased by 58%.
But as the climate changes, the questions these scientists are asking will have to change too.
As we get back on the river, the bright sun has crept behind thick clouds that accumulated through the afternoon. An unexpected storm is brewing. This has already been a surprisingly wet winter and spring – offering a badly needed reprieve for the systems and communities across the west devastated by drought, as well as more opportunity for these scientists to test new solutions. But dry days still lie ahead, along with new threats posed by a warming world.
At such close contact with this river, these scientists see the intricate details of alteration and loss. But, overall, they say, the work gives them hope.
As raindrops begin to fall on the canyon walls, I pause to marvel at the beautiful landscape and all it has already endured. This place, carved by the eons, is constantly changing. Perhaps forever shifted by the human touch, the Colorado River retains its sacred and wild nature.
“Things are going to change,” says Kennedy, “despite it being the most regulated segment of river. I tend to focus on the positives – and there are a lot of them.”
• This article was amended on 9 July 2023 to correct the name of the US Geological Survey.
